Stable lead alkyl compositions and a method for preparing the same



United States Patent 2,992,259 STABLE LEAD ALKYL COMPOSITIONS AND A METHOD FOR PREPARING THE SAME Hymin Shapiro, Baton Rouge, La., and Herbert R. Neal, Farmington, Mich., assignors to Ethyl Corporation, New York, N .Y., a corporation of Delaware N'o Drawing. Filed Dec. 8, 1959, Ser. No. 858,044 6 Claims. (Cl. 260-437) This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the thermal decomposition 0t alkyllead compounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical.

More specifically, this invention is concerned with an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commer- Patented July 11, 1961 a local overheating to a temperature above the tempera ture of decomposition of the tetraethyllead. Faulty wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated stateviz. separation, purification, blending, transportation, and storagethe likelihood of excessive thermal decomposition must be provided for and efiectively comb-atted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation, and storage.

This object is accomplished by incorporating with alkyllead compounds at relatively small quantity of a material which has the property of inhibiting alkyllead thermal decomposition. This object is also accomplished by conducting one or more of the foregoing operations in the presence of such a material. The materials which have cial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of thermal decomposition is more of a problem.

As is well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium-lead alloy with an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyllead compound so produced is in admixture with various reaction by-products from which it must be separated. Separation is eliected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due to the toxic and unstable nature of tetraalkyllead antiknock compounds, these distillation and purification operations are subject to many difliculties.

In these distillation and purification operations meticulous temperature control and exact safety measures are I of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciable. For example, decomposition of tetraethyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C. the decomposition rate increases logarithmically so that a point is soon reached Where external heat is no longer required and decomposition becomes self-propagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetraethyllead concentrate is washed and blown with air at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetraethyllead occasionally eeze and the friction developed may cause been found to possess the property are referred to hereinafter as thermal stabilizers.

The thermal stabilizers of this invention are aromatic sulfonic acids in which the aryl portion contains from 6 to about 24 carbon atoms. These thermal stabilizers when used in amount varying from about 0.25 to about 10 percent by weight of the lead alkyl product are effective in substantially retarding or preventing thermal decomposition of the alkyllead compound at temperatures above 100 C. for extended periods of time.

This invention is predicated on the discovery that the introduction of a sulfonic acid group, SO H, into the ring of an aromatic hydrocarbon containing from 6 to about 24 carbon atoms causes a very substantial improvement in the thermal stabilizing ability ofvthe, resulting compound as com-pared with the original hydrocarbon. By way of example, neither benzene nor toluene has any ability whatsoever in practical concentrations to stabilize lead alkyls against thermal decomposition at temperatures above 100 C. However benzene sulfonic acid and toluene sulfonic acid (benzene and toluene into which has been introduced a sulfonic acid group) each exert a very profound efiectiveness in this regard. This same marked improvement in eifectiveness carries over into .all aromatic hydrocarbons as above defined. For example, the effectiveness of xylene, mesitylene, naphthalene, chrysene, and like aromatic hydrocarbons is markedly improved when these compounds are converted into their sulfonic acids.

An important feature of this invention is that the present thermal stabilizers are relatively inexpensive and easily made.

Typical thermal stabilizers of this invention are pdodecyl benzene sulfonic acid; 3,5-di-'1,1,3,3-tetramethylbutyl benzene sulfonic acid; 2,4-xylene sulfonic acid; cumene sulfonic acid; cymene sulfonic acid; l-naphthalene sulfonic acid; 2-naphthalene sulfonic acid; l-anthracene sulfonic acid; Z-anthracene sulifonic acid; 9-anthracene sulfonic acid; and the like.

The chief thermal decomposition products of alkyl lead compounds are lead metal and hydrocarbon gas. Hence, a very good index of alkyllead thermal decomposition is liberation of this gas.

To illustrate the elfectiveness of this invention, direct comparisons were made between the decomposition characteristics of unstabilized and stabilized tetraethyllead. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A cc. gas buret beside the bath, and equipped with a water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of 160 C., the sample-containing tube was quickly immersed in the bath and clamped with the levelling bottle adjusted to hold the has buret in place at a zero reading. Then measured was the time during which the sample was held at 160 C. without pronounced thermal decomposition and consequent gas evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred within 1 minute as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapid ly cool it down to about 100 C. or below.

However, when to the same amount of tetraethyllead there was previously added 2 percent by weight in one instance of benzene sulfonic acid and in another instance of p-toluene sulfonic acid, no pronounced deterioration occurred at 160 C. for 40 minutes. The same order of efiectiveness subsists when repeating these experiments using 2 percent by Weight of the various xylene sulfonic acids and the various methylethyl'benzene sulfonic acids. When these experiments are repeated using naphthalene sulfonic acid and anthracene sulfonic acid even greater effectiveness against thermal deterioration at 160 C. exists. In fact, with these compounds no deterioration occurs for over 100 minutes.

The above-described beneficial behavior of the thermal stabilizers of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetrapropyllead. In. fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess alkyl halide have been discharged from the autoclave. For example, one of the above thermal stabilizers may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step which is conducted at a temperature close to the temperature where hazardous run-away decomposition is particularly prevalent. By adding one of the above thermal stabilizers to the reaction concentrate just prior to distillation, the danger arising from unexpected temeprature increases is substantially elminated.

Most preferably the above thermal stabilizers are employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least 80 percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the

addition of a small amount of thermal stabilizer to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. For example tetraethyllead, tetrarnethyllead, tetrapropyllead, dimethyldiethyllead, triethylphenyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition by incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention.

What is claimed is:

1. A method of inhibiting the decomposition of an alkyllead compound at temperatures from about C. to about C. which comprises incorporating with said cound a small amount of an aromatic sulfonic acid in which the armomatic portion contains from 6 to 24 carbon atoms sufficient to inhibit such decomposition.

2. In the process of producing an alkyllead compound by reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation, in the presence of :a small amount of an aromatic sulfonic acid in which the aromatic portion contains from 6 to 24 carbon atoms sufiicient to inhibit thermal decomposition of the alkyllead compound.

3. An alkyllead compound containing, in amount suflicent to inhibit thermal deterioration thereof at temperatures from about 100 C. to about 160 C., an aromatic sulfonic acid in which the aromatic portion contains from 6 to 24 carbon atoms suflicient to inhibit thermal decomposition of the alkyllead compound.

4. The composition of claim 3 wherein said acid is selected from the group consisting of naphthalene sulfonic acid and anthracene sulfonic acid.

5. Tetrae-thyllead containing a small amount of henzene sulfonic acid sulficient to inhibit thermal deterioration of the tetraethyllead at temperatures from about 100 C. to about 160 C.

6. Tetraethyllead containing a small amount of toluene sulfonic acid sufiicient to inhibit thermal deterioration of the tetraethyllead at temperatures from about 100 C. to about 160 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,727,053 Krohn Dec. 13, 1955 Patent No s 2,992,259

UNITED :STATES PATENT. OFFICE CERTIFICATE OF CORRECTION July '11, I961 Hymirrfihepiro et 31.

certified that error appears in the above numbered pat- It is hereby that the said Letters Patent should read as ent requiring correction and corrected below.

Column 4, line 23, for "cound" read compound Signed and sealed this 20th day of February 1962.

(SEAL) Attest: l

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES FROM ABOUT 100* C. TO ABOUT 160*C. WHICH COMPRISES INCORPORATING WITH SAID COUND A SMALL MOUNT OF AN AROMATIC SULFONIC ACID IN WHICH THE AROMOMATIC PORTION CONTAINS FROM 6 TO 24 CARBON ATOMS SUFFICIENT TO INHIBIT SUCH DECOMPOSITION. 